My ZyXEL VMG8324 arrived today... a very nice modem/router combo. It seems like it would make a very adequate all in one unit. However, for me it was being used as a modem only. I updated to the newest firmware on the ZyXEL website (V100AAKL7C0).
The improvement in download was about 200kbits and the upload was reduced by about 300kbits... so no real gain. Back to the HG612! I'll maybe give it another go later with some of the newer firmwares. I had read a few pages of the thread on the different firmwares in use, but got a bit lost given how many there are!
I took the opportunity to change the Mk3 faceplate and another RJ11 cable, just in case either of those were causing issues - apparently not. The only thing I could possibly change now is the power adapter, but given that the ZyXEL was syncing so similarly, I don't suspect that to be an issue either.
I suppose it's good to know that my line is functioning optimally. I'm quite pleased with a nearly 42mbits sync on a line that's around 1250m! Now just to get rid of this hateful interleaving and get G.INP on the line which is STILL not active... I'm not the most patient of fellows so waiting on this really isn't easy.